People in groups accused of being cults normally don't make for very objective commentators. I think it would be very difficult to find three people not directly affiliated with SGI who have a good understanding of it, who don't think it is seriously blurring the line between cult and religion.
Clearly SGI is pretty cult like, and your vast majority of Buddhist from all other traditions who have had experience with the group, tend to agree that it has a lot of cult like qualities and have trouble finding the aspects of it that would qualify it as being Buddhism.
I looked into SGI pretty heavily, I read a few of its books, and even was getting some newsletters, but it continually did things that were to me extremely cult'ish behavior. My favorite is when I got a official SGI newsletter requesting that everybody recruit at least two new members. You know what is really cult'ish about SGI, is that 98% of the suggested reading material was written by the president of SGI Daisaku Ikeda, who has a lot of cult of personality type scandals and qualities.
SGI isn't labeled a cult because it isn't Christian based, because nobody is saying Zen Buddhism is a cult or Theravada Buddhism is a cult. SGI earned the cult label by doing the stuff a cult does, it is also why it has cult survivor groups, write ups on cult awareness websites, and has many people scratching their heads about how exactly is qualifies itself as being a type of buddhism. You are "offended" because you happen to be a member of this particular cult and probably invested a lot of yourself in it.
Also, I like your tricky language... but lets be clear the group SGI started in 1975 (SGI is not the same thing as the original lay society). "The largest Buddhist school in America" sounds like some more tricky language to make it sound like SGI is the largest segment of Buddhist population... it is not, and not by a long shot. SGI makes up maybe 1% of Buddhist worldwide, and likely not much more than that in the US. Doesn't matter though, because Scientology has more members than SGI, that doesn't mean Scientology is not a cult... so size is something of a non sequitur.
I have to say though that SGI is getting better, but so are the Moonies. That's one of the benefits of fast wild growth, because if they grow too big too fast, cult groups usually have to start softening their edges to deal with the politics that arise inside them.
I know and love some SGI members as dear friends, but the more exposure they get to traditional forms of Buddhism, the more they start to realize that SGI is kind of its own animal and they got sucked into something better judgment would of told them to avoid.
Anyway, I look forward to a lengthy cult'y defensive rant. =)